Liquid crystal display with a wide viewing angle

ABSTRACT

A liquid crystal display includes a bottom substrate with thin film transistors and pixel electrodes, and a top substrate with a black matrix and color filters. Each pixel electrode has an opening pattern, and each color filter has a groove corresponding to the opening pattern. A common electrode is formed on the black matrix and the color filters, and vertical alignment layers are formed on the common electrode and the pixel electrodes, respectively. A liquid crystal layer bearing negative dielectric anisotropy is interposed between the substrates. The liquid crystal layer contains monomers, and a polymer is formed at the liquid crystal layer between the opening pattern of the pixel electrode and the groove of the color filter.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a liquid crystal display and,more particularly, to a liquid crystal display with a wide viewingangle.

[0003] (b) Description of the Related Art

[0004] Generally, liquid crystal displays have a structure where aliquid crystal layer is sandwiched between two substrates, and anelectric field is applied to the liquid crystal to control lighttransmission. Among the substrates, the top substrate is provided with acommon electrode and color filters, and the bottom substrate with thinfilm transistors and pixel electrodes.

[0005] In VA-type (vertically aligned) liquid crystal displays, theliquid crystal molecules are aligned normal to the substrates when anelectric field is not applied. In case two polarizer films are arrangedperpendicular to each other, the linearly polarized light that haspassed through the first polarizer film is completely blocked by thesecond polarizer film in the absence of an electric field. That is,since such a liquid crystal display exhibits a very low brightness at an“off” state in the normally black mode, it can obtain a relativelyhigher contrast ratio than the conventional TN liquid crystal displays.

[0006] However, when gray scale voltage is applied, the VA-type liquidcrystal display involves a narrow viewing angle because of significantdifference in retardation of the light depending on the viewingdirections.

[0007] In order to solve such a problem, it has been proposed that anopening pattern should be formed at the electrode portion. When voltageis applied to the electrode with such an opening pattern, a bentelectric field is generated at an area close to the opening pattern,called “fringe field.” The fringe field makes it possible to arrange theliquid crystal molecules in an appropriate manner, thereby widening theviewing angle.

[0008] However, in this case, a photolithography process is necessary toform an opening pattern at the common electrode on the color filters.This may damage the underlying color filters, and increase productioncost.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a liquidcrystal display with a wide viewing angle in simplified processingsteps.

[0010] It is another object of the present invention to prevent thecolor filter damage, when fabricating a liquid crystal display.

[0011] These and other objects may be achieved by a liquid crystaldisplay with the following features.

[0012] The liquid crystal display includes a first substrate, a secondsubstrate facing the first substrate, a liquid crystal layer sandwichedbetween the first and the second substrates, and first and secondelectrodes formed at either the first substrate or the second substrateto apply an electric field to the liquid crystal layer. The liquidcrystal layer has a barrier of polymer at each pixel region.

[0013] The first electrode may be formed on the first substrate, and thesecond electrode on the second substrate. The first electrode has anopening pattern at each pixel region, and the polymer barrier ispositioned corresponding to the opening pattern.

[0014] The second substrate is provided with a color filter at eachpixel region, and the color filter has a groove corresponding to theopening pattern of the pixel electrode.

[0015] A protrusion is formed on the opening pattern. Alternatively, aprotrusion or a hollow may be formed under the opening pattern.

[0016] A first vertical alignment layer is formed on the firstelectrode, and a second vertical alignment layer on the secondsubstrate.

[0017] The liquid crystal layer bears a negative dielectric anisotropy.

[0018] In a method of fabricating the liquid crystal display, the firstand the second substrates are arranged to face each other. A liquidcrystal is injected in-between the first and the second substrates toform a liquid crystal layer. A polymer barrier is formed at the liquidcrystal layer.

[0019] The liquid crystal layer contains monomers having a property oftransmitting phases when UV light is illuminated.

[0020] The method further includes the steps of forming a firstelectrode on the first substrate, and forming a second electrode on thesecond substrate. At least one of the first and the second electrodeshas an opening pattern.

[0021] The method further includes the step of forming color filterseither at the first substrate or at the second substrate such that eachcolor filter has a groove corresponding to the opening pattern.

[0022] The UV light is illuminated to the monomers through the groove atthe step of forming the polymer barrier.

[0023] The method further includes the step of forming a protrusion onthe opening pattern, or forming a protrusion or a hollow under theopening pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] A more complete appreciation of the invention, and many of theattendant advantages thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference symbols indicate the same or thesimilar components, wherein:

[0025]FIG. 1 is a schematic view of a usual liquid crystal display;

[0026]FIG. 2 is a cross sectional view of a liquid crystal displayaccording to a preferred embodiment of the present invention;

[0027]FIG. 3 illustrates the equipotential lines and the orientationstate of liquid crystal molecules when applying voltage to the liquidcrystal display shown in FIG. 2; and

[0028]FIGS. 4A, 4B, 5 and 6 illustrate the steps of fabricating theliquid crystal display shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Preferred embodiments of this invention will be explained withreference to the accompanying drawings.

[0030]FIG. 1 is a schematic view of a usual liquid crystal display. Asshown in FIG. 1, top and bottom substrates 1 and 5 are spaced apart fromeach other by a predetermined distance. Pixel electrodes 2 areinternally formed at the bottom substrate 1, and color filters 6 and acommon electrode 7 are internally formed at the top substrate 5.Vertical alignment layers 3 and 8 are formed on the electrodes 2 and 7,respectively. A liquid crystal layer 10 bearing negative dielectricanisotropy are disposed between the alignment layers 3 and 8. Polarizingplates 4 and 9 are externally attached to the respective substrates 1and 5 to polarize the light entering and leaving the liquid crystallayer 10. The polarizing axes of the polarizing plate 4 attached to thebottom substrate 1 and the polarizing plate 9 attached to the topsubstrate 5 proceed at a right angle.

[0031]FIG. 2 is a cross sectional view of a liquid crystal displayaccording to a preferred embodiment of the present invention.

[0032] As shown in FIG. 2, a pixel electrode 21 is formed on a bottomsubstrate 11 with a thin film transistor (not shown) at each pixelregion. An opening pattern 211 is formed at the pixel electrode 21, anda protrusion 31 is formed on the opening pattern 211 with siliconnitride or organic material.

[0033] A black matrix 61 is internally formed at a top substrate 51 witha metallic or opaque material to prevent leakage of light, and a colorfilter 71 is formed on the black matrix 61 at each pixel region suchthat it corresponds to the pixel electrode 21. The color filters 71 ofR, G and B are arranged at the pixel regions in a sequential manner.Each color filter 71 has a groove 711 such that the latter correspondsto the opening pattern 211 of the pixel electrode 21. A common electrode81 is formed on the black matrix 61 and the color filters 71 with atransparent conductive material. Vertical alignment layers (not shown)are formed on the common electrode 81 and the pixel electrodes 21,respectively.

[0034] A liquid crystal layer 91 bearing negative dielectric anisotropyis interposed between the substrates 11 and 51. The liquid crystal layer91 contains monomers, and a polymer 921 is provided at the liquidcrystal layer 91 between the opening pattern 211 of the pixel electrode21 and the groove 711 of the color filter 71.

[0035] When voltage is applied to the substrates 21 and 81, an electricfield perpendicular to the substrates 11 and 51 is formed at the pixelelectrode 21, and a fringe field is formed at the edge portions of thepixel electrode 21 and the opening pattern 211. As the liquid crystallayer 91 bears negative dielectric anisotropy, the long axis of theliquid crystal molecule 911 is oriented perpendicular to the electricfield. Accordingly, as shown in FIG. 2, the liquid crystal molecules 911over the pixel electrode 21 are inclined toward the opening pattern 211under the influence of the fringe field, whereas the liquid crystalmolecules 911 over the opening pattern 211 are standing erect withrespect to the substrates 21 and 51 without rotation while being fixedby the polymer 921.

[0036] The protrusion 31 formed on the opening pattern 211 makes it easyto align the liquid crystal molecules 911 as partitioned. Alternatively,a hollow may be formed under the opening pattern 211 instead of theprotrusion 31. The protrusion or the hollow is dispensable, and hence,may be selectively used.

[0037]FIG. 3 illustrates the equipotential lines and the orientationstate of the liquid crystal molecules when voltage is applied.

[0038] As shown in FIG. 3, when voltage is applied between thesubstrates, the liquid crystal molecules 911 over the pixel electrode 21are arranged parallel to the substrates 11 and 51, but those close tothe electrodes 21 and 81 are slightly inclined due to the orientationforce of the vertical alignment layers. Closer to the edge of the pixelelectrode 21 comes, more the liquid crystal molecules 911 becomeinclined toward the opening pattern 211. The liquid crystal molecules911 over the opening pattern 211 are standing erect with respect to thesubstrates 11 and 51 without rotation while being fixed by the polymer921.

[0039] In this way, the liquid crystal molecules can be aligned aspartioned in a stable manner. Furthermore, the liquid crystal moleculesat the partitioning borderline area are standing erect with respect tothe substrates by way of the polymer so that occurrence of abnormaltexture can be prevented.

[0040] A method of fabricating the liquid crystal display will be nowdescribed with reference to FIGS. 4A, 4B, 5 and 6.

[0041] As shown in FIG. 4A, a thin film transistor (not shown), and apixel electrode 21 with an opening pattern 211 are formed on a firstsubstrate 11 at each pixel region. A protrusion 31 is formed on theopening pattern 211 with an insulating material. Alternatively, theprotrusion 31 may be formed under the opening pattern 211, or a hollowmay be formed under the opening pattern 211 instead of the protrusion31.

[0042] As shown in FIG. 4B, a black matrix 61 is formed on a secondsubstrate 51 with a metallic or opaque material such as chrome, and acolor filter 71 is formed on the black matrix 61 with a groove 711 ateach pixel region. When the two substrates 11 and 51 are arranged toface each other, the groove 711 should correspond to the opening pattern211 of the pixel electrode 21. A common electrode 81 is formed of atransparent conductive material on the black matrix 61 and the colorfilter 71.

[0043] As shown in FIG. 5, the two substrates 11 and 51 are arranged toface each other, and a liquid crystal containing monomers is injectedbetween the substrates 11 and 51 to form a liquid crystal layer 91. Themonomers have a property of making phase transition under theillumination of ultraviolet (UV) light, and forming a polymer.

[0044] As shown in FIG. 6, the UV light is illuminated to the monomersfrom the top substrate 51. As the color filter 71 absorbs the UV light,the UV light passes only through the groove 711. Then, the monomers inthe liquid crystal layer 91 are aggregated toward the opening pattern211 due the UV light, and transit the phase to form a polymer 921 whileleaving only small amount of monomers on the pixel electrode 21.

[0045] Accordingly, even when the voltage is applied, the liquid crystalmolecules 911 at the area of the opening pattern 211 and the groove 711are fixed by way of the polymer 921 to prevent abnormal textures.

[0046] As described above, in the inventive liquid crystal display, anopening pattern is formed at the pixel electrode, and a protrusion isformed on the opening pattern to obtain wide viewing angle withoutincreasing the number of processing steps. Furthermore, a polymer isformed over the opening pattern to control the arrangement of the liquidcrystal molecules, in order to prevent light leakage at the borderlinearea where the liquid crystal molecules are aligned in partitions. Inthis way, occurrence of abnormal texture can be prevented.

[0047] While the present invention has been described in detail withreference to the preferred embodiments, those skilled in the art willappreciate that various modifications and substitutions can be madethereto without departing from the spirit and scope of the presentinvention as set forth in the appended claims.

What is claimed is:
 1. A liquid crystal display, comprising: a firstsubstrate; a second substrate facing the first substrate; a liquidcrystal layer sandwiched between the first and the second substrates,the liquid crystal layer having a polymer barrier at each pixel region;a first electrodeformed at said first substrate; a second electrodeformed at said second substrate; and wherein said first substrate andsaid second substrate apply an electric field to said liquid crystallayer.
 2. The liquid crystal display of claim 1, wherein said firstelectrode has an opening pattern at each pixel region and, the polymerbarrier is positioned corresponding to the opening pattern.
 3. Theliquid crystal display of claim 2, wherein the second substrate isprovided with a color filter at each pixel region, the color filterhaving a groove corresponding to the opening pattern of said firstelectrode.
 4. The liquid crystal display of claim 2, wherein aprotrusion is formed on the opening pattern.
 5. The liquid crystaldisplay of claim 2, wherein a protrusion or a hollow is formed under theopening pattern.
 6. The liquid crystal display of claim 2, furthercomprising a first vertical alignment layer formed on the firstelectrode, and a second vertical alignment layer formed on the secondsubstrate.
 7. The liquid crystal display of claim 1, wherein the liquidcrystal layer bears a negative dielectric anisotropy.
 8. A method forfabricating a liquid crystal display, comprising the steps of: arranginga first substrate and a second substrate such that the first substrateand the second substrate face each other; injecting liquid crystalbetween the first substrate and the second substrate to form a liquidcrystal layer; and to forming a polymer barrier at the liquid crystallayer.
 9. The method of claim 8, wherein the liquid crystal layercontains monomers having a property of transitting phases when light isilluminated.
 10. The method of claim 8, further comprising the steps of:forming a first electrode on the first substrate; and forming a secondelectrode on the second substrate; wherein at least one of the firstelectrode and the second electrode has an opening pattern.
 11. Themethod of claim 10, further comprising the step of forming color filterseither at the first substrate or at the second substrate, each colorfilter having a groove corresponding to the opening pattern.
 12. Themethod of claim 11, wherein the UV light is illuminated to the monomersthrough the groove at the step of forming the barrier of polymer. 13.The method of claim 10, wherein a protrusion is formed on the openingpattern.
 14. The method of claim 10, wherein a protrusion or a hollow isformed under the opening pattern.
 15. The method of claim 8, wherein theliquid crystal layer bears a negative dielectric anisotropy.